The photocurrent of intrinsic and Se-vacancy monolayer 2H-MoSe2 in zigzag direction is calculated by using first-principles method based on the Keldysh nonequilibrium Green's functional theory. Furthermore, the photo response for the circular photogalvanic effect (CPGE) and linear photogalvanic effect (LPGE) at different photon energies are investigated. The results show that the photon energy of 2.5 eV is a turning point. Lower than the photon energy of 2.5 eV, the CPGE of intrinsic monolayer 2H-MoSe2 is steadily larger than its LPGE counterpart by the amount of the absorbed photon energy. However, the curve becomes steeper as the photon energy approaches 2.5 eV and reaches the maximum at 2.7 eV. The CPGE and LPGE curves of the Se-vacancy 2H-MoSe2 also change around 2.5 eV, i.e., the CPGE is slightly smaller than LPGE with the photon energy lower than 2.5 eV and absorbs enough photon energy to become larger than LPGE with the photon energy larger than 2.5 eV. These results can be explained by the electron transition between the valence and conduction bands, which is proportional to the density of states according to the Fermi's Golden rule. In addition, we also study the relationship between the photocurrent of LPGE and CPGE and the polarization angles theta and phi. Our results have the potential to be utilized in the optimization of monolayer transition metal dihalide-based photodetectors.

To improve the processability of biphenyl phthalonitrile resin, a flexible siloxane structure was introduced into the phthalonitrile monomer through molecular design, which was then blended with a biphenyl monomer to prepare phthalonitrile alloy resins. When the ratio of phthalonitrile monomer containing flexible siloxane to biphenyl phthalonitrile monomer was 1:1, the processing window widened from 58 to 110°C, as compared to that of biphenyl phthalonitrile. Due to the introduction of the biphenyl structure into the phthalonitrile alloy resins, the initial decomposition temperature of the silicon-containing phthalonitrile resin increased from 385 to 516°C. More importantly, the phthalonitrile alloy resin exhibited a high bending strength (66 MPa) and bending modulus (3762 MPa), indicating that it could be potentially applied as high temperature structural composite matrices. Furthermore, it provides a new strategy for processing phthalonitrile resins with a high melting point and narrow processing window.

本文基于第一性原理分别计算了Fe,Ag掺杂对单层MoSe2电子结构和光电效应的影响,结果表明:与本征单层MoSe2相比,Fe,Ag掺杂体系的能带更加密集,且费米能级附近均出现了较多杂质能带;通过对分波态密度进行分析,发现其分别是由Fe-3d、Se-4p轨道和Se-4p、Mo-4d轨道所贡献.在近乎整个可见光范围内,Fe,Ag掺杂有效加强了单层MoSe2的光响应能力,其中Ag掺杂效果最好;这可以归结于掺杂显著改变了单层MoSe2费米能级附近的能带结构.即掺杂进一步减小了体系的带隙,更有利于电子跃迁,进而产生较大的光响应.研究结果可为单层MoSe2在光电器件的实际应用提供一定的理论参考.

本文采用基于非平衡态格林函数-密度泛函理论的第一性原理方法,计算了单层WSe2的光电性质.计算结果表明:在小偏压下,几乎整个可见光范围内都能产生较强的光响应,且光响应与偏振角θ 呈现完美的余弦关系,与唯象理论相符合.锯齿型和扶手椅型WSe2纳米器件均在光子能量为2.8 eV(443 nm,对应于可见光)时,能产生较大的光响应;利用能带结构和态密度分析了产生较大光响应的原因,其主要来自第一布里渊区高对称点X处的电子受激跃迁.此外,WSe2纳米器件还具有较强的各向异性和较高的偏振灵敏度;这些结果可为WSe2在光电子器件中的应用提供重要的理论参考.

The photocurrent of Ti, Nb, Ni substitution-doped monolayer 2H–WSe2 is calculated by the first-principles method based on the Keldysh nonequilibrium Green's function-density functional theory. The photogalvanic effect(PGE) photocurrent can be generated in the monolayer 2H–WSe2 under the vertical irradiation of linear polarized light, However, it is generally very small. Calculation results show that the Nb and Ti-doped systems exhibit the characteristics of semi-metal, while the Ni-doped system tends to transform into metals. The substitutional doping of Nb, Ti, and Ni atoms can effectively enhance the photocurrent and the polarization sensitivity of monolayer 2H–WSe2.This excellent performance is mainly attributed to the fact that the doping introduces multiple impurity energy bands crossing the Fermi energy level, which becomes a bridge for electronic transitions, thus effectively enhancing the photocurrent.

基于非平衡态格林函数-密度泛函理论,采用第一性原理方法,计算了VA族元素(N、P、As或Sb)掺杂单层WS2的光电效应,并解释了掺杂提高光电效应的微观机理.结果表明:在线性极化光照射下,单层WS2中可以产生光电流.由于掺杂降低了单层WS2的空间反演对称性,导致N、P、As或Sb分别掺杂的单层WS2的光照中心区产生的光电流明显提升.其中N掺杂的效果最好,掺杂后的单层WS2在光子能量3.1 eV时获得最大光电流(1.75),并且偏振灵敏度达到最大(18.1),P、As、Sb分别掺杂的单层WS2在光子能量3.9 eV时取得较大的光电流,并且有较高的偏振灵敏度.研究结果表明通过掺杂能够有效增强光电效应,获得更高的偏振灵敏度,揭示了掺杂单层WS2在光电子器件领域潜在的应用前景.

The photogalvanic effect (PGE) enables the generation of photocurrent and also offer a high polarization sensitivity in a broadband range, showing potential applications in the low-power two dimensional (2D) optoelectronics, however the photocurrent of PGE is generally small. Here, we investigated the PGE for the 2D T-d-WTe2 monolayer by employing the quantum transport simulations, and proposed the physical mechanism to effectively enhance the photocurrent of PGE at small bias voltage. The photocurrent of PGE can be generated in the 2D T-d-WTe2 monolayer when the linearly polarized light of vertical illumination was applied. In the whole visible and near-infrared range we find the biggish photocurrent which reach up to saturate for the most photon energies under a small bias. The photocurrent of junction exhibits a cosine dependence with respect to the polarization angle. The magnitude of the largest photocurrent can be evidently enhanced about 1 x 10(4) times for a photon energy of 2.4 eV than the one around 0 eV under the bias of 0.2 V in the zigzag direction, but 7 x 10(2) times at 0.9 V in the armchair direction. Moreover, a higher polarization sensitivity can be obtained. In addition, a strong anisotropy of photocurrent can be displayed between the zigzag and armchair T-d-WTe2, and that the photocurrent of zigzag direction is almost 3 times larger than that one of the armchair direction. These results show that in the visible and near-infrared range the 2D T-d-WTe2 monolayer play a potential candidate for the optoelectronics in future. (C) 2020 Elsevier B.V. All rights reserved.

Phthalonitrile resin/exfoliated hexagonal boron nitride ( h-BN) composites with high thermal conductivity were fabricated using a novel approach. The route included two steps, micro- h-BN was coated and dispersed by phthalonitrile monomers via the function of heterogeneous nucleation, and then micro- h-BN was exfoliated by heat release during the phthalonitrile curing process. The composites achieved a high thermal conductivity of 0.736W (m·K)−1 containing 20 wt% micro- h-BN, which is 3.17 times higher than that of pure phthalonitrile resin at 0.232W (m·K)−1. Compared to traditional routes, the novel preparation approach requires less BN fillers when improving the same thermal conductivity. Importantly, other thermosetting polymers can also encapsulate BN through this strategy, which paves a new way for preparing thermally conductive thermosetting polymer–matrix composites.

This paper systematically investigates the luminous properties and thermal reliability of phosphor-in-glass (PiG)-based white light-emitting diodes (WLEDs). The PiG was prepared by introducing yellow YAG:Ce 3+ phosphor embedded with borosilicate glass through screen-printing and low-temperature sintering. The effects of sintering temperature, phosphor content, and phosphor layer thickness were studied, and then the optimized PiG was achieved. This PiG-based WLED module yields a luminous efficacy (LE) of 114 lm/W, a correlated color temperature of 5524 K, and a color rendering index of 69 at the driving current of 700 mA. Furthermore, after thermal aging test at 200 °C for 500 h, the photoluminescence intensity of PiG is only reduced by 4.3%, which is much lower than the conventional phosphor-in-silicone (PiS) of 26.2%. The LE losses of PiG-based and PiS-based WLED modules are 4.2% and 12.1% after thermal aging of 1000 h at 100 °C, respectively. The aging results show that the proposed PiG exhibits superior thermal stability characteristic, which promises the excellent thermal reliability for PiG-based WLEDs.

In this paper, we present a simple and green approach to economically fabricate microlens arrays (MLAs) on fluoropolymer encapsulation for deep ultraviolet light-emitting diodes (DUV-LEDs). The MLAs can be fabricated by micromolding water condensing based porous films. By controlling the input current and working time of initiative cooling, uniform porous film with the average height of 1.58 μm and the average bottom-width of 1.12 μm was prepared. The MLA with the aspect ratio (AR) of 1.41 was fabricated by micromolding the porous film templates. In addition, the fluoropolymer encapsulation with MLA was applied for the packaging of DUV-LED. Consequently, the light output power of DUV-LED is enhanced of 7.1% by using this MLA at the driving current of 350 mA.

In order to achieve void-free and high-speed filling for through ceramic holes (TCHs) to prepare direct plated copper (DPC) ceramic substrates, copper electroplating technology combined with nano-carbon coating process was used in this work. The nano-carbon coating process was adopted to form a nano-carbon film as a conductive layer on the hole wall. For the TCH electroplating, an ameliorative plating additive mixture was proposed, which consists of accelerator thiazolyl dithio-propane sodium sulfonate (SH110), leveler nitrotetrazolium blue chloride (NTBC) and inhibitor polyethylene glycol (PEG, MW=8000). Experimental results indicate that the optimized formula of the additives is 6ppm SH110, 5ppm NTBC, and 200ppm PEG. By this optimized formula, the filling speed was further improved by duly increasing current densities. Consequently, TCHs with high aspect ratios (ARs) of 6.25 (500μm depth and 80μm diameter) were completely and void-free filled at the high current density of 1.5 ASD for 2h, which promotes the development of vertical interconnection for DPC ceramic substrates and enhances their reliability for high power packages.

A patterned packaging structure was proposed to enhance the luminous efficacy of multiple phosphor-in-glass (PiG) based white light-emitting diodes (WLEDs). In this work, a red and yellow patterned PiG was prepared by using screen-printing and low temperature sintering. The comparison experiments between the conventional mixed PiG structure and patterned PiG structure were conducted. Compared with the mixed PiG structure, the luminous efficacy of patterned PiG structure is increased by 7.7% at the driving current of 350 mA. This is a beginning of luminous efficacy enhancement through patterned phosphor layer, and it may inspire new LED packaging structures.

Thermal resistance model of packaged light emitting diode (LED) samples was proposed to investigate the thermal performances of different ceramic substrates. The thermal resistances of four metallized ceramic substrates were measured by using thermal transient tester. Consequently, the thermal resistances of TFC-Al2O3, DPC-Al2O3, DBC-Al2O3 and DPC-AlN are 8.09 K/W, 7.05 K/W, 4.78 K/W, and 1.57 K/W, respectively. Experimental results also demonstrate that fabrication process and ceramic materials can greatly affect the thermal performances of ceramic substrate.

In order to improve the luminous properties of high-power white light-emitting diodes (WLEDs), we proposed a facile preparation of patterned phosphor-in-glass (PiG) in which yellow Y3Al5O12:Ce3+ (YAG:Ce3+) and red CaAlSiN3:Eu2+ (CASN:Eu2+) phosphor parts are separated. The patterned PiGs with sector piece and concentric ring phosphor geometries were prepared by screen-printing and low-temperature sintering. Experimental results indicated that LED modules packaged by the patterned PiGs yield high luminous efficacy and excellent color quality owing to the reducing reabsorption of yellow emission by red phosphor. In addition, the angular color uniformity (ACU) of LED modules with the ring patterned PiGs are better than those of LED modules with the piece patterned PiGs. It is also discovered that the luminous efficacy and corresponding correlated color temperature (CCT) of LED module packaged by the piece/ring patterned PiG are decreased with the increasing of piece/ring number.

To enhance the optical performance of ultraviolet (UV)-excited white light-emitting diodes (WLEDs), a novel packaging structure using multi-layered red, green, and blue (RGB) phosphor-in-glass (PiG) was proposed. The RGB PiG was fabricated by screen-printing and low temperature sintering. Comparison experiments between the conventional mixed-RGB structure and proposed packaging structure were conducted. Consequently, Compared with the mixed-RGB PiG, the luminous flux of WLEDs packaged by the multi-layered PiG with the order of R-G-B increases by 8.8% at the driving current of 500 mA, and the corresponding correlated color temperature (CCT) and color rendering index (CRI) are 4065 K and 85.6, respectively.

Due to the rapid development of aerospace industry, the amount of cutting data is increasing. Establishing cutting database for aerospace industry is necessary. Therefore, this article designs the typical aerospace material database system. According to project requirements analysis and the conceptual design, nine function blocks is set. They are data management, experiment management, optimization management, cutting tool design, cutting tool simulation, knowledge base, aerospace solutions, systems management, and help. And the article describes content and processes of every function block.

According to subject needs, this article considers both processing time and production costs as the objective function. And it gets the mathematical model of the system regarding cutting force, machine power, machining accuracy and tool life as constraints. The system is developed by Visual C++ 6.0 and SQL Server 2000. The database gets reasonable cutting parameters by Hybrid Reasoning. What's more, the system optimizes the cutting parameters by using Artificial Bee Colony algorithm further. And the optimization results have been verified its correctness.